Lose games. win games. tie games? Just play. seriously. you can get tips on here (CS minions! don't push your wave unless your laner is gone or you have vision of the jungler, be aware of your matchup, your power spikes, your opponents power spikes, know what items you need to build not just in general, but against X champion/team, all that jazz) but really, play games. I lost a lot of games even though i read about the game compulsively when leveling to 30, until i got a feel for the flow of the game. You'll find yourself CSing naturally, and getting better about pushing wave or not. Feeling how the game moves is different for each person because of different mains, different playstyles, and different ranks having different metas (on a micro scale). Play games till you can feel yours.
That being said, in the bottom right corner of the client, there are master and challenger rank games that are streamed. Every time you log in, glance through it and look for your favorite few champions, or one you want to get better at. Watch the game, and watch how that player lanes and team fights. look at their build and ask yourself 'why did they buy that item?'. After a team fight, rewind and watch it slowly. watch their positioning and combos, when they decided to chase and when they pushed objectives. Those guys shot calling is (usually) insanely good. And when its not, laugh at them, then ask what went wrong, and what could they have done better. Always ask what could have been done better, it keeps you critical of yourself.